1. Field of the Invention
The present invention relates to an image-recording device which, while moving a recording material and a recording head simultaneously relatively in a main scanning direction and a sub-scanning direction, irradiates a light beam from a recording head on the basis of input image data and records an image on the recording material, and an image-recording method. More particularly the present invention relates to an image-recording device which winds the recording material on a peripheral surface of the rotating body and records an image on the recording material, with a rotation direction of the rotating body serving as the main scanning direction and an axial direction of the rotating body serving as the sub-scanning direction, and an image-recording method.
2. Description of the Related Art
Development of technologies for printing plate exposure devices which employ a sheet-form recording material, particularly a printing plate in which a photosensitive layer is provided on a support, and record an image on the printing plate with a direct laser beam or the like has been advancing. With such technologies, rapid image recording onto printing plates is possible.
In a printing plate automatic exposure device which uses the technology of image-recording onto printing plates, in a state in which a printing plate is wound onto a peripheral surface of a rotating drum, the rotating drum is rotated at high speed (main scanning), a recording head (exposure head) moves along an axial direction of the rotating drum (sub-scanning), and an image is recorded on the printing plate.
Commonly, an edge at a leading end side of winding of the printing plate has been wound on parallel to the axial direction of the rotating drum. Thus, image-writing positions in the sub-scanning direction (the axial direction of the rotating drum) do not shift, and only a little compensation is required even if there are mechanical errors. Therefore, shifting of image-writing positions has not been a problem.
However, when the rotating drum is rotated and main scanning proceeds, main scanning lines are inclined with respect to an edge of the printing plate that is orthogonal to the axis of the rotating drum. Accordingly, inclination of the main scanning lines with respect to the rotating drum has been eliminated by winding the printing plate on at an angle with respect to the rotating drum.
This angle of inclination (θ) is determined by both a number of channels of the light beam that is irradiated and a resolution. For example, if 31 channels and 1200 dpi are taken as general specifications, the inclination angle θ is determined for such specifications.
However, when specifications are changed, for example, if this resolution is changed to 2400 dpi, the inclination angle becomes θ/2, by a simple calculation. However, because the printing plate is mechanically inclined at the angle θ and wound on, an inherent inability to achieve a correlation with respect to the specifications arises.
In Japanese Patent No. 3,179,680 (below referred to as “prior technology”), the following is disclosed: a printing plate is not inclined, but image signals are supplied sequentially along inclined pixel rows, which are inclined by precisely a predetermined angle; in accordance therewith, an image-recording beam is scanned while moving continuously in a sub-scanning direction which intersects a main scanning direction; and thus inclination of a recorded image is corrected (abstracted from “effects of the invention” of the prior technology).
To explain this more specifically, as shown in FIGS. 9A to 9F, a buffer memory 400 includes storage regions 400A, 400B and 400C corresponding to, for example, three scanning lines. If a number of lines (in the sub-scanning direction) in each of these regions is a, and the number of pixels in the main scanning direction is b, then storage space corresponding to 3a·b pixels is reserved.
In order to compensate for distortion (inclination) of an image, relative addresses for writing and reading image signals at the buffer memory 400 are controlled. That is, as shown in FIG. 10, reading addresses are inclined relative to writing addresses of the buffer memory 400 in correspondence with an inclination angle θ of scanning lines L that are created by spiral scanning (refer to the broken lines in FIG. 10) on a recording material P.
In FIGS. 9A, 9B and 9C, a writing region, which is altered for each rotation of the rotating drum, is shown as a region of oblique lines. The writing region is switched between the storage regions 400A, 400B and 400C cyclically. In contrast, a reading region, which is altered for each rotation of the rotating drum, is shown as a region of oblique lines in FIGS. 9D, 9E and 9F. The reading region is cyclically switched so as not to mutually overlap with the writing region.
By repetition of this cycling, image recording can be executed without delays, and image distortion (inclination) can be eliminated.
However, the prior technology described above offers no descriptions or suggestions at all regarding the concept of winding a printing plate on a rotating drum at an angle with respect to the axial direction.
Accordingly, complex control to implement cycling based on all the specifications such that there is no mutual overlap between writing and reading of an image is continuously required. In other words, a simple relationship, in which inputted image data can be used without modification, cannot be used.